There is a mine in south africa that yielded the largest rough diamond ever found.  That stone was cut into a couple different stones and several of them were placed in the crown jewels.  The second largest cut diamond the cullman I was cut from it at 500+ carats and placed in a pin that insets into the royal scepter.  Just this week they found a 507ct rough diamond from that some mine.  It looks as if it is going to be among the best qualities ever found.  And just so you can relate it to another object for comparison in size,  it is the size of and egg.  pretty large stone huh.  they still have not established its value,  but you can be sure it will be a pretty penny.